Possible contributions form aging in neural loci to female reproductive senescence will be analyzed in rodents (Fischer 344 rats and C57BL/6J mice). The age at which the pre-ovulatory LH-surge becomes impaired will be studied by ovarian transplantation from young rodents to hosts of various ages, and by establishing the plasma estradiol threshold for inducing the LH-surge in ovariectomized rats of various ages. The possibility that long-term ovariectomy delays or prevents age changes in LH regulation will also be studied. Age-changes in brain neurotransmitter functions will be studied to determine which alterations (e.g. in hypothalamic catecholamine regulation) are causes and which are results of altered ovarian activities. Besides levels of neurotransmitters and receptors in hypothalamic, limbic, and basal gangliar loci, the regulation of catecholamine turnover by steroids and neuroleptics will be studied in aging rodents. These projects should establish if localized changes occur in catecholamine metabolism during aging in rodents and should establish the role of aging in higher centers (brain-pituitary) in the loss of ovarian cycles during aging.